3,770 research outputs found
Physiological reactions of a passenger to transportation conditions
The effect of transportation conditions on the performance capacity of a passenger were studied, in order to establish the time for his most rapid inclusion in production activity after the trip. It was concluded that the transportation conditions impair the functional condition of the passenger's organism. The restoration of the functional state to the initial level occurs mainly in the space of one day. It is shown that it is necessary to take into consideration the adaptation of the organism during transfer to another climate zone
Electronic correlations and crystal structure distortions in BaBiO3
BaBiO3 is a material where formally Bi4+ ions with the half-filled 6s-states
form the alternating set of Bi3+ and Bi5+ ions resulting in a charge ordered
insulator. The charge ordering is accompanied by the breathing distortion of
the BiO6 octahedra (extension and contraction of the Bi-O bond lengths).
Standard Density Functional Theory (DFT) calculations fail to obtain the
crystal structure instability caused by the pure breathing distortions.
Combining effects of the breathing distortions and tilting of the BiO6
octahedra allows DFT to reproduce qualitatively experimentally observed
insulator with monoclinic crystal structure but gives strongly underestimate
breathing distortion parameter and energy gap values. In the present work we
reexamine the BaBiO3 problem within the GGA+U method using a Wannier functions
basis set for the Bi 6s-band. Due to high oxidation state of bismuth in this
material the Bi 6s-symmetry Wannier function is predominantly extended
spatially on surrounding oxygen ions and hence differs strongly from a pure
atomic 6s-orbital. That is in sharp contrast to transition metal oxides (with
exclusion of high oxidation state compounds) where the major part a of d-band
Wannier function is concentrated on metal ion and a pure atomic d-orbital can
serve as a good approximation. The GGA+U calculation results agree well with
experimental data, in particular with experimental crystal structure parameters
and energy gap values. Moreover, the GGA+U method allows one to reproduce the
crystal structure instability due to the pure breathing distortions without
octahedra tilting
Electric Field Effect in Atomically Thin Carbon Films
We report a naturally-occurring two-dimensional material (graphene that can
be viewed as a gigantic flat fullerene molecule, describe its electronic
properties and demonstrate all-metallic field-effect transistor, which uniquely
exhibits ballistic transport at submicron distances even at room temperature
Stacking boundaries and transport in bilayer graphene
Pristine bilayer graphene behaves in some instances as an insulator with a
transport gap of a few meV. This behaviour has been interpreted as the result
of an intrinsic electronic instability induced by many-body correlations.
Intriguingly, however, some samples of similar mobility exhibit good metallic
properties, with a minimal conductivity of the order of . Here we
propose an explanation for this dichotomy, which is unrelated to electron
interactions and based instead on the reversible formation of boundaries
between stacking domains (`solitons'). We argue, using a numerical analysis,
that the hallmark features of the previously inferred many-body insulating
state can be explained by scattering on boundaries between domains with
different stacking order (AB and BA). We furthermore present experimental
evidence, reinforcing our interpretation, of reversible switching between a
metallic and an insulating regime in suspended bilayers when subjected to
thermal cycling or high current annealing.Comment: 13 pages, 15 figures. Published version (Nano Letters
Tetraquarks composed of 4 heavy quarks
In the current work spectroscopy and possibility of observation at the LHC of
tetraquarks composed of 4 heavy quarks is discussed. Tetraquarks concerned are
T_{4c}=[cc][cc]$, T_{4b}=[bb][bb] and T_{2[bc]}=[bc][bc]. By solving
nonrelativistic Schroedinger equation masses of these states are found with the
hyperfine splitting accounted for. It is shown that masses of tensor
tetraquarks T_{4c}(2++) and T_{2[bc]}(2++) are high enough to observe these
states as peaks in the invariant mass distributions of heavy quarkonia pairs in
pp -> T_{4c}+X -> 2J/\psi+X, pp -> T_{2[bc]}+X -> 2B_{c}+X and pp ->
T_{2[bc]}+X -> J/\psi\Upsilon(1S)+X channels while T_{4b} is under the
threshold of decay into a vector bottomonia pair.Comment: 8 pages, 3 figures, in the revised version several refences were
adde
Unconventional quantum Hall effect and Berry’s phase 2pi in bilayer graphene.
There are known two distinct types of the integer quantum Hall effect. One is the conventional quantum Hall effect, characteristic of two-dimensional semiconductor systems, and the other is its relativistic counterpart recently observed in graphene, where charge carriers mimic Dirac fermions characterized by Berry’s phase pi, which results in a shifted positions of Hall plateaus. Here we report a third type of the integer quantum Hall effect. Charge carriers in bilayer graphene have a parabolic energy spectrum but are chiral and exhibit Berry’s phase 2pi affecting their quantum dynamics. The Landau quantization of these fermions results in plateaus in Hall conductivity at standard integer positions but the last (zero-level) plateau is missing. The zero-level anomaly is accompanied by metallic conductivity in the limit of low concentrations and high magnetic fields, in stark contrast to the conventional, insulating behavior in this regime. The revealed chiral fermions have no known analogues and present an intriguing case for quantum-mechanical studies
- …